1. Field of the Invention
This invention relates generally to the treatment of psychiatric disorders by modulating the activity within appropriate regions of the cerebral prefrontal cortex, and more particularly to a method of modifying pathological electrical and chemical activity of the brain by electrical stimulation and/or direct placement of neuromodulating chemicals within the corresponding areas of the orbitofrontal cerebral cortex (OFC).
2. Description of the Prior Art
The treatment of psychiatric disorders by neurosurgical techniques has an extensive history. In the early 1930""s Fulton and Jacobsen first recongnized that an experimentally induced neurotic behavior in chimpanzees could be abolished by frontal lobectomy. Within a few years, Freeman and Watts developed the first psychosurgical procedure for humans known as the frontal lobotomy. As the inherent physiology of the frontal lobe became more evident, the original freehand procedure of Freeman and Watts became less and less extensive. By the late 1940""s, the method of stereotaxis, in which the patient""s brain is modeled in 3-dimensional space for exquisite targeting accuracy, merged with lesioning techniques resulting in an even more efficacious and safe psychosurgical procedure. Further developments of stereotactic equipment have combined with novel advancements in functional and anatomic imaging to encompass the state of the art in the neurosurgical treatment of psychiatric disorders today. However, the fundamental limitation of these lesioning techniques is that they are inherently irreverible and static in nature. There is no proverbial xe2x80x9coffxe2x80x9d switch to alleviate side effects and no way to adjust the desirable effects in response to a patient""s developing symptom profile.
Within the field of neurosurgery, the use of electrical stimulation for treating neurological disease, including such disorders as compulsive eating, chronic pain, movement disorders, has been widely discussed in the literature. It has been recognized that electrical stimulation holds significant advantages over alternative methods of treatment, for example lesioning, inasmuch as lesioning can only destroy neuronal activity. In many instances, the preferred effect is to stimulate or reversibly block neural signals. Electrical stimulation permits such stimulation of the target neural structures, and equally importantly, it does not require the destruction of the nervous tissue (it is a reversible process, which can literally be shut off or removed at will).
Another technique which offers the ability to affect neuronal function in a reversible and dynamic fashion is the delivery of drugs directly to target tissues via a subcutaneously implanted pump. Such drugs, either traditional psychiatric agents or chemicals mimicking neurotransmitters, could be instilled at such low doses as to completely avoid the side effects so common to moden pharmacotherapy. Such doses could also be tailored in magnitutde with regard to a particular patient""s varying symptomatology. A chemical neuromodulating system could be implanted as a primary treatment strategy or in combination with an electrically based one. A combination therapeutic approach, one combining electrical and chemical means, would be penultimate to generating healthy neuronal tissue itself.
To date, however, disorders manifesting gross physical dysfunction, not otherwise determinable as having emotional or psychiatric origins, comprise the vast majority of those pathologies treated by deep brain stimulation. A noteworthy example of treatment of a gross physical disorder by electrical stimulation is included in the work of Alim Benabid, and his research team, who have proposed a method of reducing, and in some cases eliminating, the temor associated with Parkinson""s disease by the application of a high frequency electrical pulse directly to the subthalamic nucleus (see Neurosurgical Operative Atlas, Vol. 8, March 1999, pp. 195-207, Chronic Subthalamic Nucleus Stimulation For Parkinson""s Disease; and New England Journal of Medicine, Vol. 339, October 1998, pp. 105-1111, Electrical Stimulation of the Subthalamic Nucleus in Advanced Parkinson""s Disease).
Conversely, direct neuroaugmentation treatments for disorders which have traditionally been treated by behavioral therapy or psychiatric drugs, has been largely limited to the stereotactic lesioning procedures mentioned above. The four lesioning techniques mostly in use today are cingulotomy, capsulotomy, subcaudate tractotomy, and limbic leucotomy. Such procedures have been applied to date in the treatment of Affective disorders and Anxiety disorders. If one critically examines the results of these procedures in the literature, it would be apparent, when applied to a carefully selected patient population in conduction with modern equipment and imaging techniques, these procedures are both efficacious and safe. In fact, in a certain subset of patients who have failed all conventional (pharmacotherapy and psychotherapy) treatments, these neurosurgical procedures are the only efficacious options available. If would follow that electrical and/or chemical neuromodulating techniques with their inherent reversibility and adjustability would an even better solution than the traditional lesioning techniques. To date, however, intracranial neuromodulation techniques have been largely unexplored. Only recently, in the Oct. 30, 1999 issue of Lancet, have Meyerson et al. described a technique for deep brain electrical stimulation of the anterior internal capsule for OCD patients. While the results are preliminary, they are also quite promising as three of the four patients had good results.
Another effort has been made to treat psychiatric disorders via peripheral nerve stimulation. A noteworthy example is the effort to control compulsive eating disorders by stimulation of the vagus nerve which has been described by Wernicke, et al. in U.S. Pat. No. 5,263,480. This treatment seeks to induce a satiety effect by stimulating the afferent vagal fibers of the stomach. For patients having weak emotional and/or psychological components to their eating disorders, this treament can be effective insofar as it eliminates the additional (quasi-normal) physio-chemical stimulus to continue eating. This is especially true for patients who exhibit subnormal independent functioning of these fibers of the vagus nerve. For compulsive eating patients who are not suffering from an insufficient level of afferent vagal nerve activity resulting from sufficient food intake, however, the over stimulation of the vagus nerve and potential resultant over abundance of satiety mediating chemicals (cholecystokinin and pancreatic glucagon) may have little effect. It has even been suggested that continued compulsive eating, despite overstimulation of the vagus nerve, may exacerbate the emotional component of the patient""s disorder. This, therefore, begs the question, is vagus nerve stimulation useful in treating the psychological component of the disorder of compulsive eating, or is it simply a method of minimizing the additional, but natural, pressures to eat because of normal physical hunger. More generally, the question may be asked, is peripheral nerve stimulation of any kind the most appropriate method of treatment for disorders which are, at the core, the result of a pathology exhibited in the brain.
If the answer to this question is that the stimulation of a peripheral nerve can result in the release of a chemical which specifically counteracts the psychological pathology, for example if the release of greater amounts of cholecystokinin and pancreatic glucagon had a direct effect on the pathology exhibited in the brain, then, for that patient, the treatment will have a greater probability of success. If, however, as is most probably the case, the increase in the level of activity of the peripheral nerve does not result in the release of such a chemical, and therefore, has no effect on the area of the brain responsible for the emotional/psychiatric component of the disorder, then the treatment will have a much lower probability of success.
The impetus, therefore, would be to treat Psychiatric disorders with direct modulation of activity in that portion of the brain causing the pathological behavior. In some manner, however, the determination of what regions of the brain are exhibiting pathological function must be determined. Fortunately, several methods for determining precisely this have been developed by a number of researchers.
Normal brain function can be characterized by four discrete frequencies of electrical output Other frequencies are almost exclusively associated with pathology. The use of magnetoencephalography (MEG scans) has permitted quantificaion of electrical activity in specific regions of the brain. It has been proposed that MEG scans may be used to identify regions exhibiting pathological electrical activity. The resolution of the MEG scans of the brain are highly accurate (sub-one millimeter accuracy), however, correlating the MEG scan with MRI images for the surgical purposes of identifying anatomical structures limits the overall resolution for surgical purposes to a volume of 10 to 30 cubic millimeters. Other techniques focus on the metabolic changes that occur in the extracellular milieu in response to neural acitivity. Such techniques include functional magnetic resonance imaging (FMRI) and positron emission tomography (PET). While such techniques lack the temporal and spatial resolution of MEG, they are able to observe activity that is sometimes unable to be seen by MEG (due to the inherent nature of the technique).
From its earliest inception, the neurosurgical approach towards the treatment of Anxiety and Affective disorders has centered around the frontal cerebral cortex. Indeed, as Freeman and Watts"" forntal lobotomy evolved, the areas of surgical intervention focused more and more on the OFC. Neurosurgeons, neurologists, and psychiatrists have found that intervention in this area afforded the most efficacious procedure while minimizing the effect on other unwanted areas. The frontal cerebral cortex based on clinical, neuropsychological, and functional imaging studies has been shown to be involved in cognitive integration and planning, features generally considered specific to the human intellect. More specifically, these studies have shown that the OFC is involved with the integration of the emotional state on the above processes. Furthermore, the OFC has been demonstrated to be involved with the internal representation of reward with regard to task completion. In laymans terms, the OFC helps mediate the feeling of accomplishment one feels when an internally generated task is completed. Neuropsychological and functional neuroimaging studies have all implicated the OFC in the pathogenesis of Affective, Anxiety, and Substance Abuse disorders. Given these findings, it is not surprising that three of the four stereotactic procedures currently in use for the treatment of Affective and Anxiety disorders (capsulotomy, subcaudate trachtotomy, and limbic leucotomy) seek to alter the output and/or input of the OFC. Taken one step further, the OFC appears to be an ideal place for the reversible and dynamic neuromodulation techniques described herein.
It is therefore the principal object of the present invention to provide a more generically applicable method for treating certain psychiatric disorders.
It is further an object of the present invention to provide a fully reversible and adjustable method of treating certain psychiatric disorders.
It is still further an object of the present invention to provide a method of treating certain psychiatric disorders the effectiveness of which may be evaluated rapidly.
It is also an object of the present invention to provide a method of interventionally treating certain psychiatric disorders while minimizing the necessary pathological investigaion.
The preceding objects are provided in the present invention, which comprises new and novel methods of treating psychiatric disorders by implantation of stimulation electrodes and/or intra-axial drug delivery catheters at specific locations in the frontal cerebral cortex. In another aspect, the present invention also comprises new and novel methods for identifying the proper positioning of the electrodes/and or catheters within the frontal cerebral cortex for a given specific psychiatric disorder. More particularly, in the first aspect, the present invention comprises a method of therapeutically treating a psychiatric disorder by surgically implanting an electrode and/or drug delivery catheter into a predetermined site within the brain of the patient, wherein the predetermined site is selected within the prefrontal cortex. Referring more particularly to FIG. 1, the orbitofrontal cerebral cortex 12 consists of a subsection of the frontal cerebral cortex 10, the most anterior portion of the brain. Specifically, the orbitofrontal cortex 12 lies medially to the inferior frontal gyrus 14 and lateral to the gyrus rectus. The orbitofrontal cortex (OFC) is also distinct cytotechtonically, corresponding to areas 10 and 11 according to the widely accepted classification scheme of Brodmann. In FIG. 2, the anatomic connections of the OFC with dorsomedial and anterior thalamic nucleii, the striatum, the pallidum, and the Papez circuit (which is thought to mediate emotional affect in man) are illustrated in a conceptual map.
The OFC has direct and reciprocal excitatory connections, presumably mediated by the neurotransmitter glutamate, with the dorsomedial and anterior thalamic nucleii. In addtion, a more indirect loop exists between the OFC, the dorsomedial thalamic nucleus, the ventromedial striatum, and the globus pallidus. Multiple connections also exist between the OFC and the limbic system. The limibc system is a group of structures in the brain which are thought to mediate the emotional state. At the core of this system is the Papez circuit, first illustrated in 1937, which includes the cingulate gyrus, the anterior thalamic nucleus, the amygdala, the fornix, and the mamillary bodies. The OFC has numerous connections with the Papez circuit via the baslolateral amygdala, the anterior thalmic nucleus and the anterior cingulate gyrus.
In the first aspect of the invention, therefore, the proximal end of the electrode and/or catheter is coupled to an electrical signal source and/or drug delivery pump which, in turn, is operated to stimulate the predetermined treatment site in the orbitofrontal cortex of the brain, such that the clinical effects of the psychiatric disorder are reduced.
In the second aspect, the present invention comprises a method of determining the proper therapeutic treatment, i.e., the proper position or placement of the electrodes and/or catheters, for a specific psychiatric disorder comprising the steps of identifying a large sampling of patients, each exhibiting a common specific psychiatric disorder and then identifying which common region of the orbitofrontal cortex exhibits pathological electrical and/or chemical activity during manifestations of the specific psychiatric disorder. The common regions demonstrating this pathological activity constitute the predetermined treatment site, whereafter a suitable means for affecting the activity of said predetermined treatment site may be employed to ameliorate the psychiatric disorder generically with a high probability of success.
In particular, the region identified above, including the orbitofronal cortex, is herein identified by its known anatomical connections and functional brain imaging as being actively involved in channeling or generating the pathological electrical activity associated with psychiatric disorders. It is important to note that this region, its functions, and its connections is a common structural feature of human brains, and therefore is a common target across a large number of patients. As suggested above, this commonality of function and structure within the orbitofrontal cortex allows for common treatment targeting, even in instances wherein different patients have other disparate locations within their brains that also exhibit pathological electrical activity.